1. Field of the Invention
This invention relates to a semiconductor manufacturing apparatus for forming various elements on a semiconductor substrate, and in particular to a lithography apparatus for forming a desired thin film pattern on a semiconductor substrate.
2. Description of the Related Art
In recent years, integration has been developed in a semiconductor device having various functioning elements formed on its semiconductor substrate made of Si or GaAs, and now LSIs (Large Scale Integrated circuits) and VLSIs (Very Large Scale Integrated circuits) are prevailing in the market. In particular, one-chip computers are used in various apparatuses such as super computers, electronic calculators, industrial robots, domestic electrical devices, etc. In addition, higher integration is being developed so as to provide ULSIs (Ultra Large Scale Integrated circuits).
Such integrated circuits as above are produced by subjecting wafers to various treatments such as thin film and resist film-forming treatments, exposure-to-light treatment, etching and doping treatments, etc. Many improvements have been made to the wafer treatment techniques so as to form highly integrated circuits on the wafer.
In the wafer processing, a photo-lithography technique is often utilized. In lithography, light of a short wavelength and of a monochromatic spectrum is used so as to prevent a reduction in resolution due to diffraction of light, thereby performing submicron-scale lithography. Further, there is a challenge to perform nanometer-scale lithography using a soft X-ray source. Moreover, though it is not suitable for mass production, there is a technique of directly drawing a fine pattern by using an electron beam having a diameter of several tens of nanometers.
In photo-lithography, a resist layer formed on a substrate is exposed to light with a contracted photomask pattern projected onto the resist layer. The wavelength .lambda., the focal depth Z, and the resolution R of a light source have the following relationship: EQU Z=.lambda./(NA).sup.2 EQU R=k.times.NA/.lambda.
where NA represents the numerical aperture of a contracting lens, and k a certain constant. If the resolution is increased by shortening the wavelength, the focal depth will be small. Accordingly, a desired resolution cannot be obtained when the region to be exposed has an uneven surface. Thus, the region must have a highly even surface. This can be achieved by using a thin film-forming technique. However, the technique requires control of high accuracy, and it would be difficult to apply the technique to production of VSLIs which includes as many as ten or more processes.
Moreover, in accordance with the development of refining techniques of patterns, high accuracy has been required also in alignment of upper and lower patterns formed repeatedly, which makes a detection device control system complex, resulting in a difficulty in performing auto alignment of a photomask pattern.
Furthermore, in lithography using electron beams, in accordance with refining of the diameter of an electron beam, electromagnetic lenses and their peripheral apparatuses have been enlarged. Thus a complex technique has been required to hold a substrate in a vacuum atmosphere, and further it has been difficult to perform etching.
Since an apparatus of a large size has low characteristic frequency, a three-dimentional relative static performance between a substrate and a mask of a light source or of a contracting optical system is deteriorated. As a result, a large vibration eliminator is required so as to avoid influence of vibration occurring outside, and an additional device for controlling distortion in the apparatus due to temperature and ambient pressure is required.
Thus, in photo-lithography using soft X rays or in lithography using electron beams, submicron scale lithography is now approaching its limit.
Incidently, STM lithography using a scanning tunneling microscope (STM) has been proposed these days, and is expected much by those skilled in the art. In the STM lithography, atoms or molecules are adsorbed onto or removed from a substrate with resolving power determined by the shape of the tip of a probe. In an ideal state, only one atom can be adsorbed onto or removed from the substrate. This technique is summarized in "The scanning tunneling microscope as a tool for nanofabrication, Nanotechnology 1 (1990) 67-80" written by G. M. Shedd et al.
In the technique, when a voltage is applied between a probe and a semiconductor wafer, a tunneling current or a field-emitted current will flow therebetween. The tunneling current is caught as an electron beam having a diameter determined by the shape of the probe tip. The diameter can be reduced to as small as 1 nm in a most desirable state. By supplying a gas consisting of atoms or molecules onto the substrate, and simultaneously applying the tunneling current (electron beam) between the probe and the substrate, the atoms or molecules can be adsorbed onto only that portion of a substrate on which the tunneling current flows. That is, a desired amount of atoms or molecules can be deposited on the semiconductor wafer, with the resolving power of the electron beam as determined by the diameter thereof. Further, molecules or atoms constituting a thin film formed on a substrate can be removed by varying the above conditions. Also in this case, removal is performed only in a portion on which the tunneling current (electron beam) flows, so that the thin film is etched with the resolving power of the beam as determined by the diameter thereof. Thus, an ultra fine thin film pattern is formed which cannot be obtained by using photo-lithgraphy.
In addition to its primary operation for obtaining a three-dimentional image indicative of the unevenness of the surface of a conductive substance, STM lithography can discriminate whether or not a substance is a metal or a semiconductor by measuring the I/V characteristic between a voltage, applied between the probe and substance, and a tunneling current flowing therebetween. Moreover, there is an atomic force microscope (AFM) which is similar to the STM and which can detect the unevenness of the surface of an insulating substance. With an AFM, instead of detection of tunneling current, that displacement in an elastic body is detected which is caused by an interatomic force exerted between a probe and a sample when the probe is approached to a point 10-0.1 nm before the sample, thereby obtaining an atom-scale three-dimensional image indicative of the unevenness of the sample surface as with an STM. Since the AFM can detect the unevenness of the surface of the insulating substance, it also can measure the isolation structure of elements in a semiconductor circuit, and the pattern of a capacitor element in the same.
In a case where STMed LSI chips are manufactured in an independent system by using STM lithography, it is required to develop a new system employing a technique higher than a submicron-scale lithography apparatus since at present there are no techniques of interfacing a nanometer-scale input/output pattern, in order, for example, to perform wire bonding or surface bonding between one STMed chip and a lead frame or a submicron-scale VLSI chip.